Seismic Characterization and Monitoring of Fresh Concrete Using Acoustic Waves

This study focuses on the seismic characteristics and behaviour of fresh concrete (water-cement ratio >2) designed for consolidation of soils, which was not really studied in the past. The propagation of acoustic waves, which constitute a potential non-destructive imaging tool in the future, was monitored and characterized using a specifically-designed experimental device during eight hours in the laboratory, to assess the evolution of the mixed material as a function of its maturity. This study highlights the very low values of P wave velocities in such a material, as well as the corresponding S waves velocities, their associated large attenuation and dispersion in the [0.5-6 kHz] frequency range. It has been found that attenuation remains the lowest when concrete mixture is younger than 90 minutes and that no velocity dispersion was detected. The study of velocity and attenuation at early age shows that the concrete has a fluid mixture with grains in suspension, and presents an elastic behaviour which stays poorly compressible during the first eight hours.